Add topics and platforms to sqlite3 package

Author: simolus3

sqlite3/pubspec.yaml

@@ -7,6 +7,20 @@ issue_tracker: https://github.com/simolus3/sqlite3.dart/issues
 environment:
   sdk: '>=2.18.0 <4.0.0'
 
+# This package supports all platforms listed below.
+platforms:
+  android:
+  ios:
+  linux:
+  macos:
+  web:
+  windows:
+
+topics:
+  - sql
+  - database
+  - ffi
+
 dependencies:
   collection: ^1.15.0
   ffi: '>=1.2.1 <3.0.0'